1. Technical Field
This invention is related to the field of internal combustion (IC) engine ignition systems. More particularly, it is related to the field of detecting an open secondary winding of an ignition coil.
2. Discussion
Typically, an ignition coil and an ignition or a spark plug are disposed in a combustion chamber of an internal combustion engine. The ignition coil includes a primary winding and a secondary winding. The ignition plug is connected in electrical series between a first end of the secondary winding and ground potential. If the spark plug is not connected (as is the case where the secondary is open), no spark will be generated, and part of the charged energy is dissipated through ringing current caused by capacitance between the secondary winding and ground. Since the charged energy is not dissipated by a spark, the fly-back energy dissipated by the IGBT over the primary winding side after the end of charge is much higher than the case when the secondary winding is connected to a spark plug and a spark occurred after the coil was charged. In fact, the total energy dissipated by the IGBT connected to the ignition coil with an open secondary winding could be as great as four times more than when the secondary winding is connected to a spark plug. This indicates that the heat dissipation of the IGBT could be four times more than the normal operational condition. A heat sink is required to protect the IGBT from being overheated for both normal operational and open secondary conditions. This increases cost of the ignition system. However, in some cases the open-secondary condition may be prevented.